1. Field of the Invention
This invention relates to field-emission (cold) cathodes and especially to rounded-end-protuberance emitters for cold cathodes.
2. Description of the Prior Art
Present field-emission cathodes, such as pointed protuberance (carbon felt) or cross-hatched types, are characterized by the fact that the emitting edges or points are sharp. Only low current densities can be handled by sharp-edged emitters since they melt and vaporize at large current densities such as are required for electron-beam-pumped lasers.
A second problem exists with pointed-end-protuberance cold cathodes. Residual gases in the device are ionized by the intense field existing at the point. Once started, ionization proceeds rapidly from cathode to anode resulting in a strong increase in current, and, if the ionization reaches the anode, can short out the cold-cathode device. Thus, this type of device can only be operated in extremely short pulse durations. The ionization results in a drop of anode-to-cathode impedance called "impedance collapse".